Recent advances in understanding the genes conferring blue-colored grains in common wheat and their use i n wheat breeding

As a staple food crop, common wheat is a major source of energy for human beings. It accounts for approximately 30% of the food and 20% of the calories consumed by humans worldwide. However, increased production of common wheat is needed to keep pace with the increasing human population and to balance decreases in wheat yield due to drought, global warming, and other environmental stresses. Therefore, the breeding of common wheat to improve stress tolerance, grain yields, and nutrient levels is important to ensure the safety of the global food supply. Grain color is attractive to both humans and other animals. and the coloration serves as a marker for crop breeding. Thus, grain color is an important agricultural trait in common wheat. Most common wheat species produce white or yellow grains, while a small number of varieties produce red, blue, or black grains due to the accumulation of anthocyanins in their endosperm, episperm, or aleurone layer. The same is true for other staple food crops, including maize, rice, and barley. However, unlike those crops, in which the genes that control grain color are present in the genome, all known blue-grained common wheat is formed by crossing common wheat with species that harbor the genes required for anthocyanin biosynthesis. Therefore, hybrid wheat with blue-colored grains has a complex genome and chromosomal origin. This means that the genes that control grain color are absent from or inactive in the common wheat genome, and this in turn makes it difficult to determine the origin of the blue grain trait in common wheat. Thus. although the anthocyanin biosynthesis pathway, which enables the production of colored grains, is conserved and induced by the transcriptional MYB-bHLH-WDR complex in maize and rice, the genes and molecular mechanism responsible for anthocyanin accumulation in hybrid blue-grained common wheat are unclear. Nonetheless, blue grains are a desired trait among wheat breeders because the coloration serves as a marker for breeding; moreover, gains containing a high anthocyanin content have health benefits for humans. Therefore, it is important to understand the cellular and molecular bases for blue-colored grains in common wheat. Here, we briefly review recent advances in our understanding of the genes and the transcriptional complex that control anthocyanin synthesis in maize, rice, and barley grains. We also discuss the origin of the genes that confer blue grains in hybrid common wheat, and we summarize the use of blue grain coloration as a molecular marker in cytogenetic analysis, molecular marker-assisted breeding, and hybrid breeding in common wheat. Finally, we discuss possible strategies for cloning the blue grain-producing genes in common wheat and the application of those genes to common wheat breeding. We also discuss the evolution of grain color and blue seed genes in common wheat and other food crops.